Processes for producing decorative and protective coatings on copper metal



United States Patent US. Cl. 148-614 11 Claims ABSTRACT OF THEDISCLOSURE A process of imparting ornamental and protective coatings oncopper and copper alloys in relatively short intervals of time. Thecopper or copper alloy is treated with sulfuric or hydrochloric acid atan elevated temperature and under pressure for 15 minutes to 24 hours toform a coating containing copper compounds.

This application is a continuation-in-part of U.S. patent applicationSer. No. 554,340, filed June 1, 1966, now abandoned.

It is a primary object of this invention to provide novel processes forcoating the exposed surfaces of copper metal, including copper alloys,with an ornamental and protective pigmented layer containing one or morecopper compounds.

Another object is to form a coating comprising at least one coppercompound upon copper metal by submerging the copper metal and alloyswithin a solution of controlled reagent concentration and/or pH underconditions of elevated temperature and pressure, preferably achieved byan overpressure of oxygen.

To form 'a coating layer comprising brochantite, CuSO -3Cu(OH) ortenorite, CuO, upon copper metal, in pure or alloy form, the copper issubmerged in an aqueous acid-solution of controlled concentration andpH, preferably containing either singly or in combinations of one ormore of the following compounds: sulfuric acid, sodium sulfate, sodiumbisulfate, and copper sulfate. The solution is heated to a selectedsuitable temperature for a predetermined time interval and is alsosubjected to an overpressure of oxygen, preferably within the generalrange of 30 to 250 p.s.i. The overpressure of oxygen not onlyappropriately pressurizes the system, but uniquely supplies an oxidizingagent which is helpful in formation of the coating.

The texture, color and/or general appearance of coatings comprisingbrochantite and tenorite may be varied by subjecting copper metal todifferent combinations and concentrations of reagents, temperatures, andpressures for various time intervals. It is postulated that a thin filmof cuprite is usually formed upon the exposed surfaces of the coppermetal over the top of which the brochantite is formed.

To form a coating of atacamite, basic copper chloride, upon coppermetal, in pure or alloy form, the copper is submerged in an aqueous acidsolution of hydrochloric acid of controlled concentration and pH. Thesolution is heated to a selected suitable temperature within the rangeof 90 C. to 95 C. for a predetermined time interval and is alsosubjected to an overpressure of oxygen, preferably within the generalrange of 60 p.s.i. to 70 p.s.i. The overpressure of oxygen not onlyappropriately pressurizes the system, but uniquely supplies an oxidizingagent which is helpful in the formation of the coating.

The time interval for maintaining the desired tempera- 3,522,109Patented July 28, 1970 tures in preparing such coatings is determined bythe desired thickness of the layer to be produced. It may vary from afraction of an hour after the desired temperature is reached to manyhours, but as much as 24 hours is rarely required. Elevated temperaturesare preferably attained through use of an autoclave, which speeds thereaction by which the coatings are produced. Decorative and protectivelayers are thus formed within a few hours or fraction of an hour incontrast to certain natural patinas which appear only after years ofweathering.

By so varying the (a) types, concentrations and pH of the reagent, (b)temperatures, (c) pressures, and ((1) time, the color of the coating ofbrochantite and atacamite can be varied anywhere between emerald greenand blackish green. The tenorite so produced is dark black but exhibitssuperior adherence to the base copper metal.

The results of laboratory testing are set forth below in Table I andTable II, and in Examples 1-4, inclusive.

TABLE I.pH RELATED TO FILM FORMATION ON COPPER Time pHi pHi Temp. O.P.HSOr 80.;- (min.) Layer 5. 9 4. 7 125 125 0 0. 5 50 Tenorite. 5. 1 5. 2125 125 0 1. 0 45 Do. 4. 6 4. 8 125 125 0 0. 5 60 Tenorite plusBroehantite. 4. 2 4. 3 125 125 0 0. 5 60 Brochantite. 3. 4. 1 129 125 00. 5 60 Do. 3. 4 3. 5 125 125 0 0. 5 30 Do. 3. 2 3. 6 125 125 0 0. 5 Do.3.2 3.6 157 1, 000 0 0. 5 30 Do. 1 3. 2 3. 3 125 0. 001 0. 1 30 Do. 1 3.2 2. 7 190 500 0. 001 0. 1 30 Do. 1 3. 2 2. 8 165 240 0. 001 0. l 30 Do.3. 2 3. 2 172 250 0. 001 0. 1 120 Do. 3. 2 3. 4 0. 001 0. 1 1, 440 Do. 13. 1 2. 9 147 1,000 0. 001 0. 1 30 Do. 1 3. 1 2. 9 150 230 0. 001 0. 130 Do. 3. 1 3. 1 125 125 0. 01 1. 0 60 Do. 3.0 3. 3 125 125 0 0. 5 60Do. 1 3.0 3. 1 125 125 0 0. 1 30 Do. 1 3. 0 3. 2 125 125 0. 001 0. 1 30D o. 3. 0 3. 2 125 125 0. 001 0. 1 30 Do. 1 3.0 3. 2 125 125 0. 001 0. 130 Do.

2. 9 3. 2 125 125 0 0. 5 60 Cuprite. 2. 7 2. 65 127 125 0 0. 5 25 Nothlng. 2. 5 2. 7 192 230 0.001 0. 1 105 Brochantitc. 2. 2 2. 4 205 2500. 001 0. 1 30 Do. 1. 9 2. 4 130 250 0. 001 0. 1 1, 260 Do. 1. 6 2. 1205 250 0. 001 0. 1 60 Do. 1.6 1. 7 218 250 0. 001 0. 1 Nothing 2 1.0 7125 125 0 0 45 D0.

1 0.01 M CuSOt added. 2 0.1 M Sulfuric Acid Only-Where:

(a) pHi is the initial pH of the solution. (b) pHi is the final pH ofthe solution. (0) Temp. is the temperature of the solution in degreeseentigrade. (d) O.P. is oxygen overpressure in pounds per square inch.(0) HSO4is the ionic bisulfate molarity added to the solution. (i) SO4isthe ionic sulfate molarity added to the solution.

TABLE II.pH RELATED TO FILM FORMATION ON COPPER pHi pHi Temp. O.P. H01Time (min) Layer 1. 8 4. 8 95 60 0. 016 180 Atacamite.

Where:

(a) pHi is the initial pH of the solution.

(b) pHf is the final pH of the solution.

(c) Temp. is the temperature of the solution in degrees centigrade (d)O.P. is oxygen overpressure in pounds per square inch.

(e) 1101 is the molar concentration of the hydrochloric acid per liter.

EXAMPLE I 3 EXAMPLE 1r Brochantite coatings on copper were also formedusing a second preferred technique by submerging the copper in aqueoussolution containing 0.1 M sodium sulfate and 0.001 M sodium bisulfate,with the pH adjusted preferably within the interval of 1.6 to 3.4 byaddition of sulfuric acid. These solutions were heated to a selectedtemperature between about 140 C. and 190 C. and the oxygen overpressureswere held at a selected level between about 125 and 1,000 p.s.i.

EXAMPLE III A covering of brochantite was formed on copper submerged insolutions of 0.1 molar sodium sulfate, 0.001 molar sodium bisulfate and0.01 molar copper sulfate with the pH adjusted within the interval 2.7to 3.3 by addition of sulfuric acid. Each solution temperature wasmaintained at a desired level between about 125 C. and 190 C. while theoxygen overpressure was adjusted to a selected value within the range ofabout 125 to 1,000 p.s.i.

EXAMPLE IV Tenorite coatings were prepared using another preferredtechnique by placing copper metal in an aqueous solution of 0.5 to 1.0molar sodium sulfate, with a pH thereof retained within the range of 4.6to 5.9. The temperature of each solution was held at about 125 C. andthe oxygen overpressure was adjusted to about 125 pounds per squareinch. before heating of the solution began.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are, therefore, to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. In a process for forming decorative and/or protective coatingscomprising copper compounds on copper-containing metals, the steps of:

placing the copper-containing metal in an aqueous acid solutioncomprising either sulfuric acid or hydrochloric acid, subjecting thesolution to an elevated temperature within the range of 90 C. to 175 C.for the sulfuric acid solution or 90 C. to 95 C. for the hydrochloricacid solution, imposing an overpressure upon the solution within therange from 30 p.s.i. to 250 p.s.i. for the sulfuric acid solution or 60p.s.i. to 70 p.s.i. for the hydrochloric acid solution; establishing andretaining the pH of the solution within the acid range not less than1.6; and removing the metal from the solution after a time interval onthe order of within the range of about fifteen minutes to twenty-fourhours.

2. In a process of synthesizing pigmented layers containing coppercompounds upon the exposed surfaces of copper metal comprisingsubjecting a heated aqueous solution as defined in claim 1 in which saidcopper metal has been immersed to an overpressure of oxygen whileholding the pH ofthe solution within the range of about 1.6 to 5.9.

3. In a process of reacting an aqueous acid solution with the surface ofcopper metal as defined in claim 1 to create an external decorative andprotective layer having at least one copper compound upon the exposedsurface of the copper metal comprising formulating said acid solutionfrom the group consisting of sulfuric acid, sodium sulfate, sodiumbisulfate, and copper sulfate or hydrochloric acid, singly or incombination, and contacting the surface of the copper metal with saidacid solution while controlling the pH of the solution, elevating thetemperature of the acid solution, and elevating the pressure exertedabove the solution.

4. A process as defined in claim 3 wherein said layer comprises coppersulfate.

5. A process as defined in claim 3 wherein said solution comprises about0.5 M sodium sulfate, the pH of the solution falls within the range ofabout 3.0 to 4.8 and said layer is brochantite.

6. A process as defined in claim 3 wherein said solution comprises about0.1 M sodium sulfate and about 0.001 M sodium bisulfate, the pH of thesolution {falls within the range of about 1.6 to 3.4 and said layercomprises brochantite.

7. A process as defined in claim 3 wherein said layer comprises cuprite.

8. A process as defined in claim 3 wherein said layer comprises a copperoxide.

9. A process as defined in claim 3 wherein said solution comprises about0.5 to 1.0 M sodium sulfate, the pH of the solution falls within therange of about 4.6 to 5.9 and said layer comprises tenorite.

10. A process as defined in claim 3 wherein said layer comprisesatacarnite, basic copper chloride.

11. A process as defined in claim 3 wherein a gas comprising oxygen isused to exert said pressure.

References Cited UNITED STATES PATENTS 258,082 5/ 1882 Langhammer1486.24 2,419,915 4/1947 Priest et al. 3,279,957 10/1966 Fink 1486.24 X3,284,249 11/1966 Osborn 148-624 FOREIGN PATENTS 535,614 4/1941 GreatBritian.

RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R.

